Known dielectric ceramic compositions are proposed in, for example, Patent Documents 1, 2, 3, and 4.
Nonreducing dielectric porcelain compositions are proposed in Patent Documents 1, 2, and 3. Basically, each of these nonreducing dielectric porcelain compositions principally contain 92.0 to 99.4 mol % of BaTiO3, 0.3 to 4 mol % of Re2O3 (Re represents at least one rare-earth element selected from Tb, Dy, Ho, and Er), and 0.3 to 4 mol % of Co2O3, and accessorily contain 0.2 to 4 mol % of BaO, 0.2 to 3 mol % of MnO, and 0.5 to 5 mol % of MgO.
Each of the nonreducing dielectric porcelain compositions can be fired without converting the structure into a semiconductor even under a low oxygen partial pressure and has a dielectric constant of 3,000 or more, and an insulation resistance of 11.0 or more in terms of log IR. Furthermore, the temperature characteristics of the dielectric constant is within the range of ±15% over a wide temperature range of −55° C. to +125° C. with reference to a capacitance value at 25° C.
Furthermore, a dielectric ceramic composition and a laminated ceramic capacitor are proposed in Patent Document 4. The dielectric ceramic composition principally contains barium titanate and accessorily contains the following elements: Re (Re represents at least one rare-earth element selected from Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), Ca, Mg, and Si. The chemical composition formula of the dielectric ceramic composition is represented by 100BamTiO3+aReO3/2+bCaO+cMgO+dSiO2. (wherein the coefficients of 100, a, b, c, and d represent molar amounts), wherein the coefficients 100, a, b, c, and d satisfy the respective relationships: 0.990≦m≦1.030, 0.5≦a≦6.0, 0.10≦b≦5.00, 0.010≦c≦1.000, and 0.05≦d≦2.00, respectively.
The dielectric ceramic composition has a dielectric constant of 3,000 or more, meets the B characteristics of JIS and X7R characteristics of EIA, and has a long accelerated insulation resistance life under high temperature and high voltage, thus resulting in excellent reliability even when the thickness of the dielectric ceramic composition is reduced.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 5-9066 (claims and paragraph No. [0009])
Patent Document 2: Japanese Unexamined Patent Application Publication No. 5-9067 (claims and paragraph No. [0009])
Patent Document 3: Japanese Unexamined Patent Application Publication No. 5-9068 (claims and paragraph No. [0009])
Patent Document 4: Japanese Patent Application No. 2001-39765 (claims and paragraph Nos. [0066] and [0067]).
In recent years, in the development of electronic technology, rapid progress has been made in the miniaturization of electronic components, and trends toward miniaturization and higher capacities of laminated ceramic capacitors have become significant. However, conventional dielectric ceramic compositions are designed on the premise that the compositions are used under low field strength. As a result, the use of a thin layer of the dielectric ceramic composition under high field strength has disadvantages of significant reductions in insulation resistance, dielectric strength, and reliability. Therefore, when the thickness of a ceramic dielectric layer is reduced in the conventional dielectric ceramic composition, it is necessary to reduce the rated voltage depending on the thickness.
In each of dielectric ceramic compositions proposed in Patent Documents 1 to 4, it is possible to provide a laminated ceramic capacitor having excellent reliability by constituting a dielectric ceramic layer composed of the dielectric ceramic composition. However, when the thickness of the dielectric ceramic layer is reduced to about 1 μm, it is disadvantageously difficult to secure the reliability of the resulting laminated ceramic capacitor.
The present invention is accomplished to overcome the above-described problems. It is an object of the present invention to provide a dielectric ceramic composition and a laminated ceramic capacitor having a high dielectric constant of 3,000 or more, a small dielectric loss of 5% or less, a temperature characteristic of the dielectric constant meeting the B properties (the rate of change of capacitance with reference to a capacitance at 20° C. is within the range of ±10% between −25° C. to +85° C.), a high resistivity of 1011 Ωm or more, and high reliability, i.e., a mean failure time of 100 hours or more in an accelerated reliability test (150° C., DC field strength: 10 V/μm), even when the thickness of the dielectric ceramic layer is reduced to about 1 μm.